It is pointed out from the data of Morgan, Sturtevant and Bridges that the mutation infra-bar of D. melanogaster acts in all combinations, including the double genes peculiar to this locus, like a bar gene with an added completely recessive effect and not at all like an intermediate between bar and wild type (round eye). For example, in all of the combinations of 4 bar or infra-bar genes, there is no significant departure from 26.1 facets except in homozygous double infra-bar (4 infra-bar genes) in which the average becomes 38.2. Similarly, all combinations with 3 bar or infra-bar genes have close to 38.3 facets provided at least 1 bar gene is present, but if all 3 are infra-bar the average is 138. This principle applies in all other cases both in cf cf and 9 9 .